Optical recording medium

ABSTRACT

The present invention relates to an optical recording medium. The optical recording medium according to one embodiment of the present invention includes a substrate, a reflective layer located on the upper side of the substrate and reflecting an incident laser beam, and an information recording layer located on the reflective layer. The information recording layer includes a first recording layer containing a compound in the form of A X B 1-X  (0.1≦X≦0.9), wherein A is one element selected from the group consisting of Ni, Ag, W and Cr, and B consists of at least one element selected from the above group except for the one element corresponding to A, and a second recording layer containing at least one element selected from the group consisting of Si, Sn, Sb and Ge. The laser beam is irradiated on the first recording layer prior to the second recording layer. Therefore, the optical recording medium of the present invention may provide high recording density and transmittance velocity suitable for BD system by combining the recording layer materials.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical recording medium. Inparticular, the present invention relates to a recordable opticalrecording medium consisting of three recording layers.

2. Description of the Related Art

With the advent of multimedia age comprehensively dealing with videosignal including moving picture and stop picture, audio signal, andcomputer data information, package media including all kinds of discslike CD and DVD have been widely used. Recently, there have been activeefforts to apply an optical recording medium to the recording media ofmobile phone, digital camera, broadcasting, and movie.

The optical recording medium is divided into read-only memory (ROM)optical recording medium, recordable optical recording medium capable ofrecording information only once, and rewritable optical recording mediumcapable of writing, reading, and deleting information repeatedly.

The recordable optical recording medium can be applied for data backupor storage of broadcasting, movie, etc. As recording layer material ofthe recordable optical recording medium, organic material like dye orinorganic material may be used. Only, in case of using the organicmaterial as the recording layer material, a problem may be occurred inlong term storage of data recorded in the optical recording medium.

As recording mechanisms of the recordable optical recording medium, a) apit is generated when the recording layer material is burned, b) a pitis formed from expansion of the volume as the recording layer materialis decomposed, c) a new phase is formed by solidifing after therecording layer is melted, and d) a new material (for example, silicide,germanium compound, or antimony compound) is formed by reaction on thecontact surface with foreign material.

Also, these mechanisms may be occurred multiply. In case the recordingmark is generated by multiple mechanisms, if a laser beam is irradiatedonto the optical recording medium, first material and second material inthe recording layer may be mixed and changed to form different materialfrom the recording layer.

In this case, data are recorded by optical property changed in therecording layer material, and the recorded data can be identified bychange of reflexibility according to the changed optical property beforeand after recording.

FIG. 1 is a sectional view illustrating the structure of a conventionaloptical recording medium. FIG. 2 is a sectional view illustrating oneform of generated record mark in case of performing land recording tothe optical recording medium of FIG. 1. And, FIG. 3 is a sectional viewillustrating one form of generated record mark in case of performinggroove recording to the optical recording medium of FIG. 1.

In FIG. 1, the optical recording medium includes a substrate 60, areflective layer 50, an information recording layer 100, an opticaltransmittance layer 10, and a dielectric layer 20, 30.

The substrate 60 plays a role to support physical form of the opticalrecording medium. As material of the substrate 60, ceramic, glass,resin, etc. are generally used, but polycarbonate resin is preferable.

The reflective layer 50 is deposited on the substrate 60, reflects laserbeam incident to the optical recording medium through the opticaltransmittance layer 10, and sends back the beam to the direction of theoptical transmittance layer 10. Therefore, it is desirable that theoptical transmittance layer 10 contains a material having highreflexibility or alloy to which highly reflexible material is added.

The information recording layer 100 is deposited on the reflective layer50, and includes a first recording layer 110 and a second recordinglayer 120.

Each material contained in the first recording layer 110 and the secondrecording layer 120 forms a new material in mixture when the laser beamis irradiated thereon. The new material has totally differentreflexibility from other materials around.

When the laser beam is irradiated, the materials of the first recordinglayer 110 and the second recording layer 120 make a recording mark inthe mechanism that they react at the contact surface to form a newmaterial.

Also, the dielectric layer 20, 30 is laminated on at least one side ofthe information recording layer 100.

In FIG. 2 and FIG. 3, the form of recording in an optical recordingmedium is explained in case of recording information by irradiating thelaser beam to the optical recording medium.

Groove and land are formed on the surface of the information recordinglayer 100, and guide the laser beam irradiated onto the opticalrecording medium.

Land recording means that data are recorded onto the convex part of theinformation recording layer 100 as shown in FIG. 2, and recording mark90 is formed on the part that the laser beam first arrives at in thesurface of the information recording layer 100.

Groove recording means that data are recorded onto the concave part ofthe information recording layer 100 as shown in FIG. 3, and recordingmark 90 is formed on the part that the laser beam later arrives at inthe surface of the information recording layer 100.

Therefore, both land recording and groove recording are possible in theoptical recording medium.

The optical recording medium in consisted of four or five layers likereflective layer 50, information recording layer 100, opticaltransmittance layer 10, and dielectric layer 20, 30. Thus, the opticalrecording medium is thick, and the manufacturing cost is increased.Especially, the reflective layer 50 contains very expensive substancelike AgPdCu or AgNdCu, and its thickness is about 700 Å to 1000 Å.Therefore, the manufacturing cost of the optical recording medium isincreased, and the thickness of the optical recording medium is thickerdue to the reflective layer 50. On the other hand, the recording mediumfor next generation requires very high recording density andtransmittance velocity for data. The size of recording mark of theoptical recording medium should be smaller than the present size toincrease the recording density recorded in the optical recording medium.Thus, a laser wavelength irradiated onto the optical recording mediumshould be reduced to 450 nm or less, and numerical aperture should beincreased to 0.7 or more. Also, the data transmittance velocity shouldbe much higher than the present one of between 30 Mbps and 35 Mbps.

In case of BD (Blu-ray Disc) that is one recording medium for nextgeneration, the recording layer material having characteristic of jitteracceptable within the ranges of recording linear velocity of between5.28 m/s and 10.56 m/s and a laser power of between 3 mW and 7 mW at 405nm wavelength should be included in the optical recording medium.

Particularly, the recordable optical recording medium having the abovecharacteristic requires combination of the recording layer material inwhich □) the contrast between recording mark and space in the opticalrecording medium should be high, □) the recording sensibility should behigh, □) the recorded mark should be stable, □) the recordingcharacteristics including noise and jitter of the recording mark shouldbe satisfied in BD system.

Also, in case the recording mark 90 is made inside the optical recordingmedium by irradiated laser, combination of the recording layer materialis required to prevent the laser power used for making the recordingmark 90 from getting too high.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an optical recordingmedium in which the information layer can be consisted of threerecording layers, the thickness can be reduced by eliminating areflective layer and a dielectric layer, and the manufacturing cost canbe saved.

Another object of the present invention is to provide an opticalrecording medium that has high recording sensibility and big contrastbetween recording mark and space as well as satisfies characteristic ofBD.

Another object of the present invention is to provide an opticalrecording medium that has superior stability of recording mark andsuperior recording characteristic of jitter as well as satisfiescharacteristic of BD.

Another object of the present invention is to provide an opticalrecording medium in which the laser power necessary for making recordingmark is low.

The optical recording medium according to one embodiment of the presentinvention includes a substrate and an information recording layerlocated on the substrate. The information recording layer includes afirst recording layer containing at least one element selected from thegroup consisting of Ag, In, Ge, Sb and Te, a second recording layercontaining at least one element selected from the group consisting ofSi, Sn, Sb and Ge, and a third recording layer containing at least oneelement selected form the group consisting of Ni, Ag, Au, W, Cr and Mo.

The optical recording medium according to another embodiment of thepresent invention includes a substrate, at least two informationrecording layers located on the substrate and a separation layer formedbetween the information recording layers. The information recordinglayers includes a first recording layer containing at least one elementselected from the group consisting of Ag, In, Ge, Sb and Te, a secondrecording layer containing at least one element selected from the groupconsisting of Si, Sn, Sb and Ge, and a third recording layer containingat least one element selected form the group consisting of Ni, Ag, Au,W, Cr and Mo.

As described above, in the optical recording medium of the presentinvention, the information layer can be consisted of three recordinglayers, the thickness can be reduced by eliminating a reflective layerand a dielectric layer, and the manufacturing cost can be reduced.

Also, the optical recording medium of the present invention may providehigh recording sensibility and contrast between recording mark and spaceas well as record data in high density. Moreover, in the opticalrecording medium of the present invention, low laser power may be enoughto make recording mark.

Further, the optical recording medium of the present invention mayprovide very stable recording mark and superior recordingcharacteristic.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawing(s) will be provided by the office upon request and paymentof the necessary fee.

The above and other features and advantages of the present inventionwill become readily apparent by reference to the following detaileddescription when considered in conjunction with the accompanyingdrawings wherein:

FIG. 1 is a sectional view illustrating the structure of a conventionaloptical recording medium;

FIG. 2 is a sectional view illustrating one form of generated recordmark in case of land recording to the optical recording medium of FIG.1;

FIG. 3 is a sectional view illustrating one form of generated recordmark in case of groove recording to the optical recording medium of FIG.1;

FIG. 4 is a sectional view illustrating the structure of the opticalrecording medium according to a first embodiment of the presentinvention;

FIG. 5 is a sectional view illustrating one form of generated recordmark in case of land recording to the optical recording medium of FIG.4;

FIG. 6 is a sectional view illustrating one form of generated recordmark in case of groove recording to the optical recording medium of FIG.4;

FIG. 7 is a sectional view illustrating one form of generated recordmark in case of land recording to the optical recording medium accordingto a second embodiment of the present invention;

FIG. 8 is a sectional view illustrating one form of generated recordmark in case of groove recording to the optical recording mediumaccording to a second embodiment of the present invention;

FIG. 9 is a sectional view illustrating the structure of the opticalrecording medium according to a third embodiment of the presentinvention;

FIG. 10A and FIG. 10B are views illustrating results of reflexibilitybefore and after recording according to the optical recording mediumsconsisted of five recording layers and two recording layers;

FIG. 11A and FIG. 11B are views illustrating horizontal temperaturedistribution after recording of the recording layer containing Ge in thetest results of FIG. 10A and FIG. 10B;

FIG. 12A and FIG. 12B are views illustrating vertical temperaturedistribution after recording of the recording layer containing Ge in thetest results of FIG. 10A and FIG. 10B;

FIG. 13 is a view illustrating result of reflexibility change of theoptical recording medium according to one embodiment of the presentinvention in case combination of thickness of the third recording layerand the dielectric layer is changed;

FIG. 14 is a view illustrating laser recording pulse waveform used fordata recording of the optical recording medium for performanceevaluation of the optical recording medium according to one embodimentof the present invention;

FIG. 15 is a view illustrating temperature distribution of the opticalrecording medium according to recording time in case of recording in therecording pulse of FIG. 14;

FIG. 16 is a view illustrating temperature distribution depending onpresence of the dielectric layer in the optical recording mediumaccording to one embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

Hereinafter, the preferred embodiments of the present invention will beexplained in more detail with reference to the accompanying drawings.

FIG. 4 is a sectional view illustrating the structure of the opticalrecording medium according to a first embodiment of the presentinvention. FIG. 5 is a sectional view illustrating one form of generatedrecord mark in case of land recording to the optical recording medium ofFIG. 4. And,

FIG. 6 is a sectional view illustrating one form of generated recordmark in case of groove recording to the optical recording medium of FIG.4.

In FIG. 4, the optical recording medium of the present inventionincludes a substrate 200, an information recording layer 210, and anoptical transmittance layer 220.

The substrate 200 plays a role to support physical form of the opticalrecording medium. As material of the substrate 200, ceramic, glass,resin, etc. are generally used, and polycarbonate resin is preferable.

The optical transmittance layer 220 contains a material having highreflexibility or alloy to which highly reflexible material is added. Alaser beam is incident to the optical recording medium through theoptical transmittance layer 220, and sends back the beam to thedirection of the optical transmittance layer 220.

The information recording layer 210 is deposited on the substrate 200,and includes a first recording layer 212, a second recording layer 214and a third recording layer 216. Each material contained in the firstrecording layer 212, the second recording layer 214, and the thirdrecording layer 216 forms a new material in mixture when the laser beamis irradiated thereon. The new material has totally differentreflexibility from other materials around.

The positions of the first recording layer 212, the second recordinglayer 214 and the third recording layer 216 in the information recordinglayer 210 of FIG. 4 may be changed each other. That is, it is notnecessary that the first recording layer 212, the second recording layer214 and the third recording layer 216 are disposed in sequence.

The first recording layer 212 contains at least one element selectedfrom the group consisting of Ag, In, Ge, Sb and Te, preferably in theform of A_(W)(Sb_(Z)Te_(1-Z))_(1-W)(0≦W≦0.2, 0.5≦Z≦0.9), wherein A isone element selected from a first group consisting of Ge, Sn, Si, Cu,Au, Ag, Pd, V, Bi, Zr, Ti, Mn and Mo.

The second recording layer 214 desirably contains at least one elementselected from the group consisting of Si, Sn, Sb and Ge. It is alsodesirable that the second recording layer 214 contains one elementselected from the group consisting of Si, Sn, Sb and Ge as main elementin 50 atomic percents (atomic %) or more.

The third recording layer 216 desirably contains at least one elementselected from the group consisting of Ni, Ag, Au, W, Cr and Mo.

When the laser beam is irradiated, the materials of the first recordinglayer 212, the second recording layer 214 and the third recording layer216 make a recording mark in the mechanism that they react at thecontact surface to form a new material.

FIG. 5 and FIG. 6 illustrate forms recorded to the optical recordingmedium in case of recording information by irradiating laser beam to theoptical recording medium according to the first embodiment of thepresent invention.

Groove and land are formed on the surface of the information recordinglayer 210, and guide the laser beam irradiated onto the opticalrecording medium.

Land recording means that date are recorded onto the convex part of theinformation recording layer 210 as shown in FIG. 5, and recording mark250 is formed on the part that the laser beam first arrives at in thesurface of the information recording layer 210.

Groove recording means that date are recorded onto the concave part ofthe information recording layer 210 as shown in FIG. 6, and recordingmark 250 is formed on the part that the laser beam later arrives at inthe surface of the information recording layer 210.

Therefore, both land recording and groove recording are possible in theoptical recording medium according to the present invention.

FIG. 7 is a sectional view illustrating one form of generated recordmark in case of land recording to the optical recording medium accordingto a second embodiment of the present invention. And, FIG. 8 is asectional view illustrating one form of generated record mark in case ofgroove recording to the optical recording medium according to a secondembodiment of the present invention.

In FIG. 7 and FIG. 8, the dielectric layer 260 may be Laminated aroundor inside the information recording layer 210 in the optical recordingmedium according to the second embodiment of the present invention

In case the dielectric layer 260 does not exist, the temperature mayrise a little at same recording power because the transmittance rate ishigh and the absorption rate is low at the time of irradiating the laserbeam.

It is desirable that the dielectric layer 260 contains at least oneelement selected from the group consisting of AN, GeN, SiN, Al₂O₃,ZnS—SiO₂, TiO and SiO₂.

The elements added to the dielectric layer 260 has good absorption, andso the transmittance rate of laser beam is decreased at the time ofirradiating the laser beam. Thus, in case the dielectric layer 260 isLaminated, the laser power necessary at the time of generating therecording mark 250 may be lowered.

Also, in case the laser beam is irradiated to the information recordinglayer 210, the dielectric layer 260 regulates temperature distributionof the information recording layer 210 by emitting heat generated in theinformation recording layer 210 in proper rate.

The dielectric layer 260 may be disposed on at least one side of theinformation recording layer 210 or inside the information recordinglayer 210.

The other constitution is the same as the optical recording mediumaccording to the first embodiment.

FIG. 9 is a sectional view illustrating the structure of the opticalrecording medium according to a third embodiment of the presentinvention.

In FIG. 9, the optical recording medium according to the thirdembodiment of the present invention includes a substrate 200, aseparation layer 240 located between two and more information recordinglayers 210, 230 and each information recording layer 210, 230, and theoptical transmittance layer 220.

Recording mark 250 may be formed in the information recording layers210, 230 as described FIG. 5 to FIG. 8.

The information recording layers 210, 230 need not have the samestructure. Thus, the dielectric layer 260 may be further included inonly one of the information recording layers 210, 230.

Hereinafter, applicability of the optical recording medium of thepresent invention will be described, comparing reflexibility and heatdistribution between optical recording medium consisting of five layers(hereinafter, referred to as “optical recording medium of five layers”)and optical recording medium consisting of two layers (hereinafter,referred to as “optical recording medium of two layers”).

FIG. 10A and FIG. 10B are views illustrating results of reflexibilitybefore and after recording information according to the opticalrecording medium of five recording layers and that of two layers. FIG.11A and FIG. 11B are views illustrating horizontal temperaturedistribution after recording the recording layer containing Ge in thetest result of FIG. 10A and FIG. 10B. And, FIG. 12A and FIG. 12B areviews illustrating vertical temperature distribution after recording therecording layer containing Ge in the test results of FIG. 10A and FIG.10B.

The optical recording medium of five layers includes the reflectivelayer 50 and the dielectric layers 20, 30 besides the two recordinglayers 110, 120, like the other optical recording medium describedabove.

The optical recording medium of two layers consists of two informationrecording layers.

The optical recording mediums of five layers and two layers includeinformation recording layers containing Ge and Au.

In FIG. 10A and FIG. 10B, the optical recording medium of two layersindicates satisfactory reflexibility difference before and afterrecording.

In FIG. 11A and FIG. 11B showing the horizontal temperature distributionof the recording layer containing Ge, temperature is concentrated at thelaser center in the optical recording medium of two layers, but diffusedrelatively widely to front and rear, and right and left in the opticalrecording medium of five layers. In case the optical recording medium offive layers, thermal interference may be occurred among recording marks,and so the optical recording medium of two layers is better in terms ofmark control.

Only, in the optical recording medium of two layers, temperature is lessincreased at same recording power because there is no thick layer at thetime of irradiating the laser, and so the transmittance rate can be highand the absorption rate can be low. This can be complemented by coatingthe dielectric layer 260.

Referring to FIG. 12A and FIG. 12B showing the horizontal temperaturedistribution of the recording layer containing Ge, temperature isconcentrated at the laser center, and heat loss to right and left isless, and thus mark control is more effective, in the optical recordingmedium of two layers. In case of the optical recording medium of fivelayers, more heat is exited to front and rear, and right and left sincethe thick reflective layer 50 has big thermal conductivity, and sotransformation of the substrate by heat may be reduced. On the otherhand, temperature is concentrated in the optical recording medium of twolayers to cause transformation by heat. This can be complemented bycoating the dielectric layer 260.

Therefore, the optical recording medium of two layers has satisfactoryproperties in reflexibility and heat.

Hereinafter, test results to the optical recording medium according tothe first to third embodiments will be described.

First, the structure and recording layer material of the opticalrecording media used for the tests will be described.

The optical recording media used in the tests include a substrate 200 ofa doughnut form of 15 mm of internal diameter, 120 mm of externaldiameter, and 1.1 mm of thickness, and 0.32 μm of track pitch havingland and groove is formed on the substrate 200.

The substrate 200 is made of polycarbonate, and multiple thin layers arelaminated on the substrate 200 in the order of the third recording layer216, the dielectric layer 260 consisted of ZnS—SiO₂, the secondrecording layer 214, and the first recording layer 212.

Also, the optical transmittance layer 220 is adhered by a polycarbonatecover sheet of 80 μm with PSA glue of 20 μm onto the first recordinglayer 212. In the lamination, the thickness of the dielectric layer 260is 200 Å, that of the third recording layer 216 is 300 Å, that of thesecond recording layer 214 is 30 Å, and that of the first recordinglayer 212 is 90 Å.

The conditions of the above tests according to the first to thirdembodiments of the present invention are described below.

In the tests, the constant linear velocity of the optical recordingmedia is 5.28 m/s, and the measuring position of the optical recordingmedia was 30 mm from the inner circumference. The data recording to theoptical recording medium was groove recording, the wavelength of laserbeam used therein is 408 nm, and the reproduction power is set at 35 mW.Also, as test apparatus, ODU-1000 of Pulstec Co., Ltd was used.

In Table 1, combination of materials of the information recording layer210 and the dielectric layer 260 in the optical recording medium asshown above and test results thereof are explained below. TABLE 1 TheThe 8T Start The first second third The modulation DC test Mark Testrecording recording recording dielectric (I8_(pp)/I8H) power stabilityNO. layer layer layer layer (%) determination (mW) determinationdetermination 1 GeSbTe Si Ag ZnS—SiO₂ 45 ◯ 3.0 □ ◯ 2 GeSbTe Ge AgZnS—SiO₂ 40 □ 1.8 ◯ □ 3 GeSbTe Sb Ag 50 ◯ 1.5 ◯ □ 4 GeSbTe Sn Ag 50 ◯2.7 □ ◯ 5 AgInSbTe Si Au ZnS—SiO₂ 55 ◯ 1.0 ◯ □ 6 AgInSbTe Ge Au ZnS—SiO₂52 ◯ 1.4 ◯ □ 7 AgInSbTe Sb Au 38 □ 2.0 ◯ ◯ 8 AgInSbTe Sn Au 40 □ 4.0 □ □9 GeSbTe Si Cr 54 ◯ 3.5 □ ◯ 10 GeSbTe Si W 50 ◯ 4.0 □ ◯ 11 GeSbTe Si Ni40 □ 4.0 □ ◯ 12 GeSbTe Sb Mo 40 □ 3.0 □ ◯

The first recording layer 212, the second recording layer 214 and thethird recording layer 216 were consisted of GeSbTe, Si and Ag,respectively, as main element in Test 1; GeSbTe, Ge and Ag in Test 2;GeSbTe, Sb and Ag in Test 3; GeSbTe, Sn and Ag in Test 4; AgInSbTe, Siand Au in Test 5; AgInSbTe, Ge and Au in Test 6; AgInSbTe, Sb and Au inTest 7; AgInSbTe, Sn and Au in Test 8; GeSbTe, Si and Cr in Test 9;GeSbTe, Si and W in Test 10; GeSbTe, Si and Ni in Test 11; and GeSbTe,Sb and Mo in Test 12.

The test standards according to each test combination are difference ofreflexibility of the optical recording medium according to 8Tmodulation, start DC test power, and mark stability. The resultsaccording to each standard of Table 1 are marked as ‘∘’, ‘□’ or ‘x’ inthe right column of each test standard (own column for mark stability)in the order of test combination showing favorable result.

First, 8T modulation indicates difference of reflexibility between spaceand mark.

That is, the difference (I8_(pp)) between minimum reflexibility valueand maximum reflexibility value to the 8T modulation pulse of the laserbeam divided by maximum reflexibility value (I8H) is expressed inpercent (%). In the 8T modulation test of laser beam, the difference ofreflexibility is the first standard of the optical recording medium.Thus, as its difference of reflexibility is bigger, the opticalrecording medium is determined more appropriate.

In the test to the optical recording medium according to the presentinvention, the difference of reflexibility between space and mark ofTest 5 was the best as 55%.

Start DC test power is a determination standard that can indirectlyconfirm whether the optical recording medium having optimized structurecan be recorded as prescribed recording power (Pw).

BD should generate the recording mark 250 at the laser recording powerwithin the range of less than 7 mW to 1×, 2× velocity of the opticalrecording medium. For indirect confirmation thereof, by measuring powerthat any change in the information recording layer 210 begins, if themeasured power is between 1.5 mW and 2.5 mW, the optical recordingmedium is determined to have proper recording sensibility to theprescribed laser power.

Hereinafter, a specific method of measuring start DC test power asdetermination standard will be described.

First, laser beam of space power (Ps(mW)) is irradiated to the opticalrecording medium. Pulse of the laser beam is single pulse type, notmultiple pulse type. And, in case the laser beam is irradiated, theoriginal size of reflexibility of the optical recording medium ismeasured as laser power to initiate change in the oscilloscope. The sizeof the measured laser power is the value of start DC test power.

In the test, the optical recording medium is determined to be optimizedif the start DC test power is less than 2.5 mW. In the test, the valueof the start DC test power was shown the best in Test 5, second best inTest 6, and third best in Test 3.

As a determination standard of the test, mark stability is a standard todetermine whether the recording mark 250 can be maintained for a longtime without any change in time. The size of recording mark 250 shouldbe maintained without growing bigger or smaller in time under effect ofthe laser beam of regenerative power or at room temperature when therecording mark 250 was formed to the optical recording medium by thelaser pulse of 8T modulation.

In the test, the recording mark 250 in the recording layers was changedin Test 2, Test 3, Test 5, Test 6 and Test 8. Thus, the material of therecording layers 212, 214, 216 may be improved by material ratio of therecording layer 212, 214, 216 and structure of the optical recordingmedium.

According to the three test results, the combinations of Ag, In, Ge, Sb,Te, and Ag, In, Ge, Sb, Te, and Ag, Au, Cr, Mo as the first recordinglayer 212, the second recording layer 214 and the third recording layer216, respectively, were evaluated as the best materials for theinformation recording layer 210. However, combination of most of theabove materials has a little large start DC test power, and so they maybe more desirable for the information recording layer 210 if there is away to lower the recording laser power a little bit more.

Hereinafter, the combination of GeSbTe, Si and Ag was selected as mainelement of the first recording layer 212, the second recording layer 214and the third recording layer 216 among the combinations of Ag, In, Ge,Sb, Te, and Ag, In, Ge, Sb, Te, and Ag, Au, Cr, Mo selected as propermaterials through the above tests, and the test results to improvereflexibility and recording sensibility to the optical recording mediumgiving the above combination will be described in detail.

FIG. 13 is a view illustrating result of reflexibility change of theoptical recording medium according to one embodiment of the presentinvention in case the combination of thickness of the third recordinglayer and the dielectric layer is changed.

In FIG. 13, the horizontal axis indicates the thickness of the thirdrecording layer 216 as □ unit, the vertical axis indicates the thicknessof the dielectric layer 260 as □ unit, and the value in FIG. 13indicates reflexibility according to thickness of the third recordinglayer 216 and the dielectric layer 260.

The optical recording medium used in the above test designed HTL (Highto Low) reflexibility, as can be seen by reflexibility difference in thepart of mark and space.

The test was conducted for two cases that the dielectric layer 260consisted of ZnS—Si0 2 (number two of FIG. 13) was not included when thethird recording layer 216 is 300□ and that the dielectric layer 260 islaminated by the thickness of 200□ (number one of FIG. 13), to considerheat variation of the substrate 260 by selecting two areas of highcontrast.

FIG. 14 is a view illustrating laser recording pulse waveform used fordata recording of the optical recording medium for performanceevaluation of the optical recording medium according to one embodimentof the present invention.

In FIG. 14, the recording power (Pw) of the laser pulse used forrecording of the optical recording medium was 5.7 mW, the space power(Ps) was 1.5 mW, and the bottom power (Pb) was 0.1 mW. The laserrecording pulse has random multi pulse from 2T to 6T, and recording wasdone by modulating the pulse to make N-1 partition pulse to eachrecording pulse.

FIG. 15 is a view illustrating temperature distribution of the opticalrecording medium according to recording time in case of recording by therecording pulse of FIG. 14. And, FIG. 16 is a view illustratingtemperature distribution depending on presence of the dielectric layerin the optical recording medium according to one embodiment of thepresent invention.

In FIG. 15, one, two and three figures indicate temperature distributionin vertical section of the track center of the optical recording mediumat each time of one, two and three figures of FIG. 14.

The temperature distribution of FIG. 15 shows that the optical recordingmedium according to the present invention forms a middle form oftemperature distribution of the optical recording mediums of two layersand five layers.

That is, in case the reflective layer and the dielectric layer do notexist like the optical recording medium of the present invention,satisfactory property can be achieved. In FIG. 16, temperaturedistribution of the front edge and rear edge of 2T shown FIG. 14 issimilar regardless of presence of the dielectric layer 260. Therefore,the dielectric layer 260 need not be laminated in the optical recordingmedium according to the present invention.

The superiority of performance of the optical recording medium accordingto the present invention is shown in a case that the informationrecording layer 100 is one (1). However, it is same when there are twoor more information recording layers 100, 200. One or more informationrecording layers in two or more information recording layers 100, 200may be combined by constitutional element, thickness ratio, sum ofthickness, etc., as shown above.

From the preferred embodiments for the present invention, it is notedthat modifications and variations can be made by a person skilled in theart in light of the above teachings. Therefore, it should be understoodthat changes may be made for a particular embodiment of the presentinvention within the scope and the spirit of the present inventionoutlined by the appended claims.

1. An optical recording medium for recording information by a mechanismforming a substance having different reflexibility from surroundingsubstance in an information recording layer through an irradiated laserbeam, comprising: a substrate; a reflective layer located on the upperside of the substrate and reflecting an incident laser beam; and aninformation recording layer located on the reflective layer, wherein theinformation recording layer includes: a first recording layer containinga compound in the form of A_(X)B_(1-X) (0.1≦X≦0.9), wherein A is oneelement selected from the group consisting of Ni, Ag, W and Cr, and B isconsisted of at least one element selected from the group except for theone element corresponding to A; and a second recording layer containingat least one element selected from the group consisting of Si, Sn, Sband Ge, wherein the laser beam is irradiated on the first recordinglayer prior to the second recording layer.
 2. The optical recordingmedium of claim 1, wherein B of the first recording layer contains atleast one element selected from the group consisting of Ge, Sb, Te, Aland Cu.
 3. The optical recording medium of claim 1, wherein theinformation recording layer includes at least one first recording layerand at least one second recording layer, and the first recording layerand the second recording layer are laminated in turn.
 4. The opticalrecording medium of claim 1, wherein the thickness of the informationrecording layer is between 90 Å and 200 Å.
 5. The optical recordingmedium of claim 1, wherein the ratio of thickness of the first recordinglayer to the second recording layer is two and more.
 6. The opticalrecording medium of claim 1, wherein the information recording layerfurther includes a recording sensibility promotion layer formed on atleast one side of the information recording layer and containing atleast one element selected from the group consisting of Sn, Zn, Pb, Bi,TI, Te, Se, S, Al, Ga, Ge, Cd, I and In.
 7. The optical recording mediumof claim 1, further including a dielectric layer formed on at least oneside of the information recording layer.
 8. The optical recording mediumof claim 7, wherein the thickness of dielectric layer formed on thefirst recording layer is 80 nm or less.
 9. The optical recording mediumof claim 7, wherein the thickness of dielectric layer formed on thesecond recording layer is 50 nm or less.
 10. An optical recording mediumfor recording information by a mechanism forming a substance havingdifferent reflexibility from surrounding substance in an informationrecording layer through an irradiated laser beam, comprising: asubstrate; a reflective layer located on the upper side of the substrateand reflecting an incident laser beam; at least two informationrecording layers located on the reflective layer; and a separation layerformed between the information recording layers, wherein the informationrecording layer includes: a first recording layer containing a compoundin the form of AXB1−X(0.1≦X≦0.9), wherein A is one element selected fromthe group consisting of Ni, Ag, W and Cr, and B is consisted of at leastone element selected from the group except for the one elementcorresponding to A; and a second recording layer containing at least oneelement selected from the group consisting of Si, Sn, Sb and Ge, whereinthe laser beam is irradiated on the first recording layer prior to thesecond recording layer.
 11. The optical recording medium of claim 10,wherein B of the first recording layer contains at least one elementselected from the group consisting of Ge, Sb, Te, Al and Cu.
 12. Theoptical recording medium of claim 10, wherein the information recordinglayer includes at least one first recording layer and at least onesecond recording layer, and the first recording layer and the secondrecording layer are laminated in turn.
 13. The optical recording mediumof claim 10, wherein the thickness of one of the information recordinglayers is between 90 Å and 200 Å.
 14. The optical recording medium ofclaim 10, wherein the ratio of thickness of the first recording layer tothe second recording layer in one of the information recording layers istwo and more.
 15. The optical recording medium of claim 10, wherein theratio of thickness of the first recording layer to the second recordinglayer in one of the information recording layers is different from thatof another information recoding layer.
 16. The optical recording mediumof claim 10, wherein the sum of thickness of the first recording layerand the second recording layer in one of the information recoding layersis different from that of another information recoding layer.
 17. Theoptical recording medium of claim 10, wherein one of the informationrecording layers further includes a recording sensibility promotionlayer formed on at least one side of the information recording layer andcontaining at least one element selected from the group consisting ofSn, Zn, Pb, Bi, Tl, Te, Se, S, Al, Ga, Ge, Cd, I and In.
 18. The opticalrecording medium of claim 10, further including a dielectric layerformed on at least one side of one of the information recording layers.19. The optical recording medium of claim 18, wherein the thickness ofdielectric layer formed on the first recording layer is 80 nm or less.20. The optical recording medium of claim 18, wherein the thickness ofdielectric layer formed on the second recording layer is 50 nm or less.